One of the operations which is normally performed during the outage of a nuclear boiling water reactor is the decontamination of the reactor cavity. This is considered to be a "critical path" operation as opposed to a "collateral" operation. In other words, it is an operation which must be performed before the succeeding operation can be undertaken and, thus, adds directly to the length of the shutdown period.
Decontamination of boiling water reactor cavity and storage pit walls is achieved by the spraying of high pressure water on the walls. The manner in which this is conventionally achieved is by lowering a man into the cavity or pit in a container suspended from a crane. He then proceeds to wash down the wall with a high pressure hose. It is desirable to use very high pressure water for this purpose, for example, up to 10,000 psi. However, the high reaction forces acting upon a container at the end of a relatively long cable cause the container and workman to be bounced from side to side. The man, even though wearing protective gear, is exposed to highly contaminated water droplets in a highly radioactive environment. The radioactivity, coupled with the sheer physical stress, makes this a very difficult and undesirable job. Because of the reaction forces, it is usually necessary to reduce the water pressure below its optimum value. As a result, the decontamination period is substantially increased and may be, for example, on the order of 8 hours.
As reactor shutdowns are very costly, it would be highly desirable to shorten the time for decontamination. It would also, of course, be desirable to reduce or eliminate the exposure of personnel to the dangers and stress-inducing features of the conventional decontamination washdown.